I have not officially entered the N-Prize (not yet anyway), so anyone can say if they would use a balloon or not.

Just for the record, if I do enter the N-Prize, I would use a balloon launched rocket. A balloon can easily take a rocket to about 30KM, which is above 95% of the earths atmosphere. As there will be little friction, the rocket can be made much smaller and therefore cheaper. GPS technology can easily track the balloon and fire the rockets when the right altitude is reached. To learn more about weather balloons, I did a search on DIY weather balloons and read about peoples ballooning projects. Also, the JPAerospace has been an inspiration. They indend to go all the way to space with balloons...

Balloon/platform adds cost to the overall budget (unless you plan on retrieving it, then it does not count, only the gas to fill it), subject to drift in the upper atmosphere (this might not please the authorities when trying to present a launch plan etc.), rocket has to be a-ok the entire time while it floats up to altitude, something comes up, not easily fixable. If your not doing the RV prize I personally think the money is worth putting into your booster, which you are making anyway so just uprate that for a ground launch.
My 2 cents.

For the N-prize, a balloon launch is probably too complicated. The aim is only to get 20g to orbit, so a cheap, disposable SRB could give you most of your velocity and get you above the atmosphere (NOTE to NASA: if you are attmepting to create an RLV, do NOT use SRBs). If the aim is to launch something bigger, though (such as a 100kg satellite or a small crew shuttle), the gains from a high-altitude Airlaunch outweigh the negatives.

So, when I do finally enter the N-prize, I'll be using a ground launched SRB. Hopefully I could get it at an angle where it's going slowest through the thickest part of the atmosphere, to reduce frictional heating.

So, when I do finally enter the N-prize, I'll be using a ground launched SRB. Hopefully I could get it at an angle where it's going slowest through the thickest part of the atmosphere, to reduce frictional heating.

You could use different grain patterns to give a different characteristic of the burn, like the shuttle SRBs. They have a star shaped grain segment in the foward, to provide high thrust at lift off and then a double truncated cone shaped grain for the rest which reduces the thrust by about 1/3 for going Max Q.

For the N-prize, a balloon launch is probably too complicated. The aim is only to get 20g to orbit, so a cheap, disposable SRB could give you most of your velocity and get you above the atmosphere.

So, when I do finally enter the N-prize, I'll be using a ground launched SRB. Hopefully I could get it at an angle where it's going slowest through the thickest part of the atmosphere, to reduce frictional heating.

Your arguments are compelling, especially after seeing the price of balloons. I have a few questions though:

1. What fuel do you intend to use for the SRB's, sugar propellant?
2. How many stages do you intend to use?
3. Will you be using solid fuel for all of the stages?

I know you guy's know we are looking at the balloon launch it's no secret, anyway how do you know it's so hard to balloon launch? Just guessing? We intend to find out. Why dont you ask JP Aerospace what they think about a balloon launch? I haven't because we intend to find out for ourselfs. They have a blog you know. I have no idea what they would say for an N-Prize attempt rockoon. But they are the ones with the experience so far. If you really want to know.

I agree with you that a balloon launch is better for small rockets, but I think the max rocket weight is around 25Kg to 50Kg. Anything heavier than that would require an unreasonably large balloon.

The N-Prize 20gram satellite could be put into orbit with a rocket weighing less than 25Kg, if launched from a balloon. It would require a much larger rocket if launched from the ground.

The mass and impulse of a rocket is proportional to it's volume, but the drag force scales by the frontal area. This means that the drag acceleration decreases linearly with the scale of a rocket. That's why a small model rocket doesn't go as high as a large high power rocket with the same shape, propellant and mass fraction.

Some people have proposed launching cubesats from a balloon, but that's just crazy. A cubesat has 50 times the mass of the N-Prize satellite, and it would require a balloon the size of the Hindenburg to lift the rocket to 100K feet.

I think balloon launches are good for about twice that but not good for much above that. They are excellent for space shots however good for quite a few miles into space.

Monroe

1.5 million cubic feet is about optimum for balloons that can be launched regularly. A program that can launch these regularly can accomplish a good deal of work. Carrying two people or rockoons and scientific payloads.

For cubesats you need air launch from a reusable UAV like Pegasus.

For more than that go with Space-X falcon-1 then 9

I'm interested in the first two beyond that I still don't see any good being done by me. I'd like to do regular space shots do some manned missions to near space and launch cubesats regularly.

1.5 million cubic feet is about optimum for balloons that can be launched regularly.

1.5 million cubic feet is a big balloon. That's 15 times the volume of a typical hot air balloon. You could launch payloads of a few kilograms into suborbital space trajectories. You might be able to launch 250 gram payloads into orbit from it.

Sure, but that's not a practical payload. Not yet anyway. Inflated yeah, they are pretty big but in the box you can easily carry one in a regular truck 2 of them if you leave the tailgate down. Size is relative and 1.5 Mcft is not as much gas at sea level so that size balloon is about the same as handling a regular hot air balloon. I have crewed for a hot air balloon one entire summer (season) and it's not the big deal everyone thinks it is to launch the balloons. It's fun too! Balloons have their use and it's the best way to do a space shot bar none. I'm sure. Orbital launches do need to be done like the Pegasus though it's a much better arrangement so our NASA or FAA shot will be developing a UAV that can launch a cubesat and be recovered on the landing strip at Matagorda. That's why Aeronautic Enterprises is the name of the company most of the work we do is in the atmosphere balloons and flying launchers are not astronautic developments. I'd rather leave the payloads up to the customers. Yep, for the n-prize the balloon launch makes it work but that's about it for rockoon launches, space shot's all day long but orbital cansats will require something different to be practical. Ground launches of cubesats is not practical and I doubt it ever will be. The falcon 1 is about as small as practical Elon did the job there if you want a launcher for something bigger than a cubesat you need one of those or one very similar. He needs some competition to get the cost down as I see it.

Josh The UAV is practical experience for the next step. A flying launcher for larger payloads. Making what I have planed work will give us practical experience moving into that phase of development don't you think? Balloon orbital launches are not practical for anything other than the N-Prize.